Activation of Src tyrosine kinases occurs in response to oxidative, heat, and UV stress, all stress stimuli that promote the formation of lens cataract. We have found that inhibition of Src family tyrosine kinases (SFKs) blocks the development of lens opacity. In this proposal we will identify the molecular mechanisms by which SFK activation induces cataract formation. Our long term objectives are to identify the alterations in signaling pathways that lead to lens disease. The signaling intermediates in these networks are likely candidates for pharmaceutical intervention to suppress the formation of lens opacities. Key to understanding how the activation of SFKs leads to cataract formation is the delineation of SFK functions in normal lens differentiation and development. We will determine the mechanisms whereby SFKs regulate cadherin function in the developing embryonic lens. To extend these studies to the pathophysiology of lens cataract, we will examine the structural and functional targets of inappropriately activation of SFKs, focusing on cadherin junction destabilization, using two Src-induced lens disease models. One is an in vitro model in which lens cell cultures are transformed with a temperature sensitive v-Src kinase with which we will dissect the molecular affects of Src activation on the stabilization and function of lens cadherin junctions at different stages of development. These studies will be paralleled in a whole lens culture model that closely approximates stress-induced cataract. In this model we will be able to link the molecular changes that result from the inappropriate activation of SFKs with the formation of lens opacities. We hypothesize that one mechanism by which SFKs influence lens cell differentiation is through their regulation of cadherin complexes and that inappropriate regulation of the SFK signaling pathways induces lens cataracts by destabilizing cadherin junctions. We propose to 1) determine the mechanisms whereby Src family kinases regulate cadherin function in normal lens cell differentiation; 2) determine the mechanisms whereby constitutive activation of the Src kinase interferes with the structure and function of lens cadherin junctions, using v-Src transformed lens cell cultures as a model for stress-induced lens disease; and 3) determine the mechanisms whereby the inappropriate activation of Src family kinases, through their targeting of cadherin junctions, induces formation of lens cataracts.